Throttle motor bearings require greases that can withstand extreme operating conditions. An automobile grease having stable properties at temperatures ranging between −40° C. and 180° C. is desired. These temperatures are at the extreme limit of what is experienced in the coldest regions and the hottest desert regions where the throttle motor will likely be used. A bearing grease composition used in an electronically controlled throttle motor for an automobile must be low torque (especially rotational torque at low temperatures), have excellent noise properties, exhibit little leakage (or evaporation), have longevity, and operational capability at low temperatures and high temperatures (between −40° C. and 180° C.).
Fluorine-based greases have been used in bearings to satisfy these stringent requirements. Fluorine greases of the prior art contain perfluoropolyether base oils, tetrafluoroethylene copolymer fillers and trace amounts of antirust agents and corrosion inhibiting agents. In situations demanding low temperature properties, a straight-chain perfluoropolyether with excellent low temperature properties has been used. However, these fluorine greases cannot satisfy the more demanding high-load/low-torque properties and durability requirements of recent years. In order to meet these far more stringent requirements, a grease composition has been proposed (Japanese Unexamined Patent Disclosure [Kokai] No. 7-102274) which contains a liquid fluorinated polymer and a filler containing hexagonal lattice boron nitride powder with a diphasic granularity distribution. While this grease composition has excellent heat-resistance and durability, it does not exhibit low temperature torque properties. There is still a need in the art for improved bearing greases for throttle motors.